Sure, the idea behind a revocable trust is it can be edited or terminated at any time...
However, things are a bit more complicated in regards to NFA items than with traditional assets. Specifically as the rules and regulations pertaining to NFA items take precedence over normal trust proceedings. Some are obvious such as a revocable trust can NOT be legally terminated at "any time" if it is still in possession of NFA items as these items can't legally exist without being assigned to an entity. Others enter a less black and white arena such as when and how often a trust can be edited.
We can argue and/or discuss our interpretations till we're blue in the face, but that doesn't make any of them factual. Hence, my use of words like "could be" and "unlikely" rather certain terms such as "will" or "can". Until we have a formal ruling from the supreme court there can be no certainty. Thus... as I suggested earlier it's a matter of proceeding at your risk tolerance level.